Recent data indicate that in an average year, not a virulent year like the current one, one or two children per thousand, who are under age two, may be hospitalized with flu. “That adds up,” she says. “It’s common enough that from a public health perspective it’s large, yet rare enough that from an individual pediatrician’s perspective it’s not that much.” Even more surprising, according to a recent unpublished CDC-sponsored study by Griffin and Edwards, 74 percent of infants and toddlers hospitalized with flu were otherwise healthy and not considered “high risk” for complications.

The CDC estimates that the annual associated costs from influenza—including doctor visits, hospitalizations, medicines, days lost from work, child care, etc.—exceed $12 billion a year. Moreover, the burden of disease from children with the flu is actually greater than that in people over 65. Griffin says that new rapid viral diagnostic tests have also raised awareness about how much flu is in the population at any given time.

The obvious solution would be that all people of all ages, who can safely do so, should receive all vaccines all of the time. Unfortunately, obstacles to the production and delivery of vaccines make that impossible.

FluMist, the nasal mist vaccine that uses a live, attenuated virus, was actually developed 10 years ago, but only became available to the public in 2003. One reason for the delay is that any new vaccine must first be tested in 30,000 to 40,000 people before it is approved for general use, making clinical trials extremely expensive and cumbersome. Another issue is vaccine safety.

“No one is willing to tolerate any kind of adverse event anymore,” Edwards says. “The reason the nasal flu vaccine is not licensed for kids under five is because some kids who’d gotten the nasal flu vaccine had some wheezing—although it’s probably the best way to vaccinate little kids. We’re in a real bind because we need to be innovative, but we have more controls and more obstacles to licensing products.”

“One of the things going on in vaccine development today is that we are taking on harder targets to immunize against,” says James Crowe, M.D., professor of Pediatrics at Vanderbilt and an expert on respiratory syncytial virus (RSV), the leading cause of lower respiratory tract disease, such as wheezing and pneumonia, in infants under two months of age. Rather than target viruses that spread through the blood, such as measles, investigators are now trying to attack viruses like RSV that cause disease at the mucosal surface but never enter the blood—a much more difficult proposition, Crowe says.

Targeting children

An experimental inactivated RSV vaccine candidate developed in the 1960s enhanced rather than prevented disease, and was not further studied in humans. Newer, safer live, attenuated vaccine candidates can generate a good immune response in children older than six months, but not in younger infants—those at greatest risk for complications from RSV infection.